1. Field of the Invention
This invention relates to plasma display panels, and especially to a method of driving plasma display panels.
2. Description of the Related Art
In general, a plasma display panel (abbreviated to “PDP” below) has a flat structure and a high display contrast without flickering. Moreover, it has many characteristics: for example, it can be made into a relatively big screen, it has a fast response, and, being of the self-fluorescent type, it can be made to fluoresce in multi-color by the use of phosphors. For this reason, its application has been expanding in the fields of large size public display device and color television, etc., in recent years.
By its method of operation, PDP has the alternating current discharge type (AC type), in which, the electrodes are covered by a dielectric substance, and is operated by a condition of alternating current discharge indirectly, and the direct current discharge type (DC type), in which, the electrodes are exposed to the discharge space, and is operated by a condition of direct current discharges. Furthermore, in the alternating current discharge type, there is the memory drive type that uses the memory of the discharge cells as its drive method, and the refresh drive type that does not use that method. Moreover, the brightness of PDP is approximately proportional to the number of discharges, that is, the repetition number of the pulse voltage, regardless of the memory drive type or the refresh drive type. In the case of the refresh drive type, as the display capacity becomes larger, brightness decreases and it is mainly used for PDP with small display capacity.
FIG. 1 is a perspective exploded view showing an example of the structure of the display cells in an alternating current discharge memory drive type PDP that is disclosed in Japanese Patent No. 2629944 (Japanese Unexamined Patent Publications No. 2-220330) and Japanese Unexamined Patent Publication No. 2000-39866.
This PDP seals the discharge gas in between two insulator plates 1 and 2 of the front surface and the rear surface made of glass plates. On the internal surface of the insulator plate 2, the transparent sustain electrodes 3 and the bus electrodes 4, which are placed coincident with the sustain electrodes 3 to reduce electrode resistance, are formed.
On the dielectric substance layer 11 between the separation walls 7, and the side surfaces of the separation walls, phosphor 8 is coated. To display the various colors, the phosphor 8 is painted and arranged into the three primary colors of red, green, and blue. In between the insulator plates 1 and 2, a discharge gas space 6 filled with a discharge gas of helium, neon, xenon and the like, or combinations thereof, is formed.
The ultraviolet light generated by the discharge of the foregoing discharge gas is converted into the visible light 12 by the phosphor 8.
The vertical separation walls are formed in between the neighboring data electrodes 5, and the horizontal separation walls are formed along the bus electrode 4 of every sustain electrode 3, cutting across the center part. Every sustain electrode 3 becomes an electrode shared by the upper and lower display cell.
FIG. 2 shows a vertical cross-sectional view of the display cells in the alternating current discharge memory drive type PDP shown in FIG. 1. The discharge operation of the selected display cells will be explained with reference to FIG. 2.
When a pulse voltage that is higher than the discharge start voltage between the sustain electrode 3 on one side of every display cell and the data electrode 5, is applied to start the discharge, according to the polarity of this pulse voltage, positive and negative electrical charges are attracted to the internal surface of the dielectric substance layers 9 and 11 on both sides, and an accumulation of electrical charges occurs.
The equivalent internal voltage due to the accumulation of electrical charges, that is, the wall voltage, decreases the effective voltage inside the cell as well as the growth of the discharge, because of its opposite polarity to the foregoing pulse voltage. Even if the foregoing pulse voltage maintains a constant value, the discharge cannot be maintained, and will eventually stop.
After that, a sustain discharge pulse that is a pulse voltage of the same polarity as the wall voltage is applied between a neighboring sustain electrode pair and as the contribution of the wall voltage, being an effective voltage, is superimposed and even the voltage amplitude of the sustain discharge pulse is low, thus, discharge start voltage can be superseded and discharge occurs.
Consequently, by continuing the application of the sustain discharge pulse between the sustain electrode pair alternatively, it is possible to maintain the discharge. This function is the aforementioned memory function.
FIG. 3 is an explanatory drawing showing the schematic structure of the PDP formed by arranging in a matrix the display cells shown in FIG. 2.
PDP 13 is a dot matrix panel for display use, in which display cells 14 are arranged into m×n rows and columns. The sustain electrodes E1, E2, . . . , Em are placed mutually in parallel as row electrodes. The data electrodes D1, D2, . . . , Dn are placed orthogonally with respect to the sustain electrodes as column electrodes.
FIGS. 4 and 5A to 5E show respectively the drive waveform chart and modal drawing showing the change of the charged condition in the priming discharge period for the foregoing PDP disclosed in Japanese Patent Unexamined Publication No. 9-244573.
In FIG. 4, WEa, WEb, WEc, WEd are sustain electrode drive pulses applied to the sustain electrodes Ea, Eb, Ec, Ed. Wd is a data electrode drive pulse applied to data electrodes Di (1≦i≦n). Sustain electrodes Ea indicates the (1+4K)-th sustain electrodes E1, E5, E9 . . . , and sustain electrodes Eb indicates the (2+4K)-th sustain electrodes E2, E6, E10 . . . , and sustain electrodes Ec indicates the (3+4K)-th sustain electrodes E3, E7, E11 . . . , and sustain electrodes Ed indicates the (4+4K)-th sustain electrodes E4, E8, E12. Here, K is 0 or a positive integer. In FIGS. 5A to 5E and later mentioned FIGS. 5F to 5H, the symbol ┌⋆┘ in the figure represents discharge.
A drive period consists of a priming discharge period, a write discharge period, and a sustain discharge period. By repeating these, desired image displays can be obtained.
To obtain stabilized write discharge characteristics in the write discharge period, the priming discharge period is a period to reset the previous history, and to generate active particles and wall charges in the discharge gas space. The write discharge period is a period in which, according to the display data, the ON/OFF of the display cells are selectively discharged. The sustain discharge period is a period in which discharges in the display cells selected in the write discharge period are repeated, and brightness is controlled.
In the priming discharge period, the sustain electrodes are divided into four electrode groups. The first group consists of the combination of the (1+4K)-th sustain electrodes counting from one side (the side of the foremost line) of the electrode arrangement. The second group is the combination of the (2+4K)-th sustain electrodes. The third group is that of the (3+4K)-th sustain electrodes, and the fourth group is that of the (4+4K)-th sustain electrodes. Here, K is 0 or a positive integer. FIG. 4 shows the drive waveforms of these four groups of sustain electrodes Ea, Eb, Ec, Ed and the data electrodes.
First, at timing (a) of FIG. 4, priming discharge pulse Pp1 of positive polarity is applied to sustain electrodes Eb, Ed to produce discharges in all the lines. Through this, as shown in FIG. 5A, in between sustain electrodes Ea, Ec, and sustain electrodes Eb, Ed, the polarities of the wall charges are different, and between the two lines corresponding to each of the sustain electrodes, charge conditions of the same polarity are formed. That is, taking the separation walls as mirror surfaces, the charge condition at every sustain electrode has mirror symmetry. With the mirror symmetry intact, when a scan pulse Pw is applied to each electrode, two lines would have been selected.
To break the mirror symmetry, at timing (b) of FIG. 4, priming discharge pulse Pp2 of negative polarity is applied to the sustain electrode Eb, and at the same time, priming discharge pulse Pp3 of positive polarity is applied to the sustain electrode Ec. Moreover, at timing (c) of FIG. 4, priming discharge pulse Pp3 of positive polarity is applied to the sustain electrode Ea, and at the same time, priming discharge pulse Pp2 of negative polarity is applied to the sustain electrode Ed. The peak values of the priming discharge pulses Pp2, Pp3 are chosen to be values that would be sufficient to generate discharges only by applying both of the priming discharge pulses Pp2, Pp3, as illustrated in FIGS. 5 B and 5C.
By the above, as shown in FIG. 5C, in all the lines, in the dielectric substance layer inside a unit fluorescent domain, wall charges of the negative polarity exist on one side in the column direction. And on the other side, as wall charges of the negative polarity actually do not exist, a charge condition that charges the opposite polarity (positive polarity here) is formed.
Next, at timing (d) of FIG. 4, priming discharge elimination pulse Ppe of positive polarity is applied to the sustain electrodes Ea, Ec, and at timing (e), priming discharge elimination pulse Ppe of positive polarity is applied to the sustain electrodes Eb, Ed to produce elimination discharges to remove unwanted wall charges. Under this condition, if the sustain electrodes are sequentially selected one by one, and a scan pulse of negative polarity Pw is applied, in lines where wall charges of negative polarity exist, opposite discharges occur. Moreover, for practical line scans, selecting sequentially from the second sustain electrode in the electrode arrangement will be acceptable.
FIGS. 5F to 5H are drawings showing the charge conditions due to write discharge and sustain discharge.
FIG. 5F represents a summary of the write discharge of every display cell (timing (f)), and the charge condition is after the finish of the writing of all the display cells. At the end of priming discharge, on the parts of the sustain electrodes where charges are not accumulated, when scan pulses of negative polarity is applied to the neighboring sustain electrodes that, in pairs, form the display cells, to produce opposite discharges, because of the 0 V potential kept, negative charges accumulate.
At timing (g), when the first sustain pulses are applied to the sustain electrodes Ea, Ec, the wall charges formed by the write discharge will be superimposed onto the potential difference between the sustain electrodes due to the sustain pulse, sustain discharges occur in the display cells formed by Eb-Ec and Ed-Ea. That is, sustain discharges occur at every other line, and, as a result, the wall charges accumulated on each sustain electrode are unified to be positive or negative.
At timing (h), when the second sustain pulse is applied to the sustain electrodes Eb, Ed, as the wall charges in all display cells will be superimposed onto the potential difference between the sustain electrodes due to the sustain pulse, sustain discharges occur in all the written-in display cells.
After that, by applying sustain pulses alternatively onto Ea, Ec and Eb, Ed, sustain discharges are repeated simultaneously in all the written-in display cells.
In the foregoing conventional drive method, between the odd-numbered and even-numbered lines, there is difference in the number of discharges in the priming discharge period. Hence, in every drive period, techniques like shifting the application objects of the priming discharge pulses Pp2, Pp3 and the priming discharge elimination pulse Ppe with respect to the previous period is necessary.
Moreover, in the priming discharge period, as discharge occurs as much as three times, as shown in FIGS. 5A to 5E, therefore, there will be a lot of light emission. As light emission due to priming discharge becomes constant background brightness independent of the display data, degradation of contrast will result if it becomes too great.
Furthermore, while sustain discharge starts at every other line with a lag of one time, they all stop at the same time. As a result, in one drive period, the number of sustain discharges is different for every line, and brightness becomes different.
Japanese Unexamined Patent Publication No. 10-3280 has suggested a plasma display panel in which first electrodes are grouped into K-th electrodes and (K+1)-th electrodes wherein K is an even number, and second electrodes are grouped into M-th electrode and (M+1)-th electrodes wherein M is an even number. The K-th and (K+1)-th electrodes and the M-th and (M+1)-th electrodes are simultaneously driven in both reset and address periods. In sustain periods, a phase of a pulse in the K-th and M-th electrodes is retarded by 180 degrees relative to a phase of a pulse in the (K+1)-th and (M+1)-th electrodes.
Japanese Unexamined Patent Publication No. 10-207417 has suggested a method of driving a plasma display panel, in which reset discharges are carried out at different timings in fields, and a discharge is not carried out in a reset period in a discharge cell which does not contribute to displaying.